Horsepower and torque are the most common terms used to define an engine’s performance but not many people know the exact role they play. Though some people can comprehend the general premises of horsepower and torque, their definitions, their history, their applications, the mathematical equations used to find their values, and how and why manufacturers use each, isn’t as well known. Here’s something to help you understand the underlying differences between the two.
What is Torque?
Torque is the measure of the force that can cause an object to rotate about an axis. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study. Whichever the field of study, it represents the capability of a force to produce change in the rotational motion of the body. In US mechanical engineering,torqueis defined mathematically as the rate of change of angular momentum of an object.
In cars and related mechanical engines, torque is a rotating or twisting force produced by an engine’s crankshaft. In simpler terms, torque can be defined as an engine’s ‘pulling force’ and helps a vehicle with initial acceleration.
Torque (also called moment — mostly by engineers) is calculated by multiplying force and distance. The SI units of torque are newton-meters, or N*m (even though these units are the same as Joules, torque isn’t work or energy, so should just be newton-meters). For example, if you use a one-foot-long wrench to apply 10 pounds of force to a bolt head, you’re generating 10-pound-feet of torque. Note that torque is measured in pound-feet, and horsepower is measured in foot-pounds per second.
At a given vehicle weight, a high torque means the vehicle can accelerate faster and is more responsive. Although not always true, generally, the more torque produced by an engine, the more work potential it has. Similarly, an engine that produces more horsepower generally has a greater ability to generate higher torque.
What is Horsepower?
Horsepower is a popular imperial unit of power of an engine. It is defined as the work done by a person or machine per unit amount of time. The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. It is a unit of power that compares the power of a machine to the muscle power of the horse.
In earlier days it was used to measure steam engine power output compared to the power of draft horses. But later on, its usage was expanded to different types of piston engines, electric motors, turbines, and other machinery.
Horsepower is measured by a dynamometer, which is a rotor in a housing. It takes a certain amount of power to make the rotor go around at a certain speed.
If you put a car into neutral, and then floor the engine while it is attached to a dynamometer, the device puts a load on the engine and sees whether it can turn the load or how fast it can turn the load around. If you run the engine at 5000 rotations per minute, (rpm), you see how much load turns on the dynamometer to calculate horsepower.
Horsepower formula is given as:
Horsepower (HP) = (Torque × Speed)/5252
Horsepower vs Torque: Key Differences
| Points of Comparison | Horsepower | Torque |
| Description | Horsepower means the total power output of the engine. | Torque expresses the turning ability of the engine (the ability to turn its flywheel). |
| Element of Time | Horsepower is a measurement of power – referring to an amount of energy transfer over time. | Torque is the measure of the force that can cause an object to rotate about an axis. It doesn’t take into account the aspect of time. |
| Formulae | Horsepower (HP) = (Torque × Speed)/5252 | Torque can be calculated as Force X Distance. |
| SI Units | The SI unit for horsepower is foot-pounds per second. | The SI units of torque are newton-meters or Pound-feet. |
Key Takeaways
- Torque expresses the turning ability of the engine (the ability to turn its flywheel) and horsepower means the total power output of the engine.
- In very simple terms, torque is the force you feel pushing you back in your seat on acceleration, while horsepower is the speed achieved at the end of that acceleration.
- Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors.
- Horsepower is a measurement of power – referring to an amount of energy transfer over time.
- Horsepower is energy output over time, and torque is instantaneous.
- Both horsepower and torque can be measured in a number of different ways, e.g. in Brake HorsePower, Power Standard, Newton Metre, Watts, Pound/Feet etc..
- Torque can be calculated as Force X Distance.
- Horsepower (HP) = (Torque × Speed)/5252
- Note that torque is measured in pound-feet, and horsepower is measured in foot-pounds per second.